1. Field of the Invention
The present invention relates to a hydraulic valve control device for heavy construction equipment, capable of leading a small amount of a high pressure hydraulic fluid drained upon descending a hydraulic actuator toward an actuator-holding spool and a main spool to prevent the actuator from being abruptly descended when the main spool is placed in neutral or switched.
2. Description of Prior Art
FIG. 1 shows main parts of a conventional hydraulic valve control device for heavy construction equipment. As shown in FIG. 1, the hydraulic valve control device for heavy construction equipment has a hydraulic pump, an actuator 15 connected to the hydraulic pump and driven upon the supplies of hydraulic fluid, a poppet 10 for opening and closing a path 12 supplying to the actuator 15 the hydraulic fluid discharged from the hydraulic pump and a path 13 communicated with the actuator 15, a back-pressure chamber 16 communicated with an orifice 11 of the poppet 10 and for storing hydraulic fluid discharged from a large chamber 15a of the actuator 15, and an actuator-holding spool 2 switched to the left or right direction based on an application of a pilot signal pressure Pi and for draining the hydraulic fluid of the back-pressure chamber 16 into a hydraulic pump through a variable orifice 5 communicated with a path 8.
A reference numeral 3 not described in the drawing denotes an elastic member for pressure-supporting the spool 2 and elastically biasing the closed drain port 7 in an initial state, and 9 an elastic member for pressure-supporting the poppet 10 and elastically biasing the path 12 of the main spool and the path 13 of the actuator 15 which are closed in an initial state.
The high-pressure hydraulic fluid drained from the large chamber 15a upon the descent of the actuator 15 is discharged into the back-pressure chamber 16 through the path 13 communicated with the large chamber 15a and an orifice of the poppet 10, and, at the same time, the pilot signal pressure Pi flows in the pilot port 6 to displace the spool 2 to the left direction of the drawing, so the variable orifice 5 is communicated with the drain port 7.
Accordingly, the high-pressure hydraulic fluid discharged into the back-pressure chamber 16 is drained into the hydraulic tank through the path 8, variable orifice 5, and drain port 7 in order, so that, when the actuator 15 is ascended from the ground, stopped, and descended again, a phenomenon that the actuator 15 is abruptly descended in an initial stage is developed to deteriorate its manipulations, to thereby cause a problem adding fatigue to drivers in case of performing coupling work in a state that heavy pipes are lifted.
Further, when in a neutral position of the spool 2, it is kept all the time that the high-pressure hydraulic fluid on the side of the back-pressure chamber 16 is communicated with the variable orifice 5 of the spool 2, so that the high-pressure hydraulic fluid of a neck portion of the spool 2 gets leaked through an annular gap on the left or right side. That is, a severe fluid leakage occurs through the annular gap between a cover 1 and the spool 2.
At this time, since the amount of fluid increases as the pressure increase, a leakage amount of fluid increases as a work device has more loads, so that the actuator 15 is automatically lowered toward the ground with a time lapse, to thereby cause a problem worsening the safety of heavy equipment.
FIG. 5 is a graph for showing leakages of hydraulic fluid based on the strokes of the main spool.
As shown in FIG. 5, if a switching timing of the actuator-holding spool 2 comes first compared to the opening timing of the main spool based on the opening timing of the main spool, the actuator 15 is abruptly descended by the quantity of fluid drained from the large chamber 15a of the actuator 15 as in xe2x80x9cAxe2x80x9d.
In the meantime, if the actuator-holding spool 2 is opened after the opening timing of the main spool as in xe2x80x9cBxe2x80x9d, the pressure of the back-pressure chamber 16 over the poppet 10 is transferred, as it is, over the poppet 10 due to the influence of the back pressure formed as the quantity of fluid increases.
Accordingly, the poppet 10 does not normally and smoothly move upwards, and experiences vibrations when the poppet 10 moves based on the back pressure changes, and the actuator 15 also undergoes oscillation and hunting phenomena in descent-stop-descent-stop forms when descending, to thereby cause a problem loosening driver""s attention during work to increase his fatigue and worsening work efficiency.
Accordingly, problems exist in that it is difficult to design to get the opening timing of the main spool and the operation timing of the actuator-holding spool 2 coincident coincident with each other and an abstruse structure thereof worsens design drawings.
It is an object of the present invention to provide a hydraulic valve control device for heavy construction equipment, capable of enhancing the manipulations of the equipment by preventing an actuator from being abruptly descended even when a main spool remains neutral or switches through feeding back toward a main spool part of high-pressure hydraulic fluid drained when an actuator is descended.
It is another object of the present invention to provide a hydraulic valve control device for heavy construction equipment, capable of enhancing design drawings through a design regardless of the timings of the main spool and actuator-holding spool which are associated to each other with a small leakage amount of fluid through a gap between a block and the spool.
It is yet another object of the present invention to provide a hydraulic valve control device for heavy construction equipment, capable of reducing drivers"" fatigue and greatly enhancing workability by enabling smooth descents of an actuator.
In order to achieve the above objects, the hydraulic valve control device for heavy construction equipment of the present invention comprises a hydraulic pump; an actuator connected to the hydraulic pump and driven upon hydraulic fluid supplies; a main spool mounted in a path between the hydraulic pump and the actuator and switched upon a pilot signal pressure to control start, stop, and direction switching of the actuator; a poppet mounted to be opened and closed at a path between the main spool and the actuator and preventing the actuator from being descended; a spool mounted between a back-pressure chamber and a feedback path of the poppet and switched upon an application of the pilot signal pressure to communicate the back-pressure chamber with a path on an outlet of the main spool; and a fluid flow-reducing path connecting the back-pressure chamber and the spool and communicating the back-pressure chamber with the feedback path upon the switching of the spool to reduce hydraulic fluid drained from the actuator.
Preferably, a diameter of the fluid flow-reducing path is formed to be relatively smaller than a diameter of the path at the outlet of the main spool.
Further, an orifice communicating the actuator with the back-pressure chamber is formed in a left and right symmetry on the poppet.